You can modify script to add this feature.
there are sites who charge for asking questions like http://www.mahalo.com/answers/
the purpose is, user want to offer money to get best answer from the community. This is good way to promote user to answer questions.
by doing this, every user will try to give his best shot for the answer, this will help to build great answers site.
This solution may not work for the sites with low traffic and low user base.